The present invention relates to a method for exposure control and method for display of a diaphragm value and/or shutter speed in a shutter speed priority mode and in a programmed mode in a multimode photographic camera such that a signal representative of information peculiar to an individual interchangeable lens is subjected together with the other exposure factors to arithmetic processing to effect exposure control or display of a shutter speed and/or a diaphragm value.
The present invention presupposes an exposure control system in a camera body which system is, in turn, based on a specified lens (hereinafter referred to as a reference lens). When a desired interchangeable lens (hereinafter referred to as a desired lens) other than the reference lens has been mounted on said camera, some deviations are inevitable between the reference lens and said desired lens--for example, light intensity error in the film plane and light intensity error as measured at the position of a photometric element (hereinafter collectively referred to as the primary quantity of error) and the difference in the fully opened aperture. Such quantities of error need to be compensated for in some manner and the present invention provides a method for exposure control and a method for display of diaphragm value and/or shutter speed to meet this need.
In the shutter speed priority mode, if diaphragm control is directly based on a diaphragm value calculated from information on brightness of an object to be photographed, said information provided by a photometric element exposed to the light coming from said object through a desired lens actually mounted on said camera, information on shutter speed given as a resistance value as a shutter dial is operated, and information on film sensitivity given also as a resistance value as a film sensitivity dial is operated, there would occur an inevitable error and no appropriate diaphragm control would be possible, because the exposure control system in the camera body is constructed on the basis of the reference lens. This is true also in case of the programmed mode.
The present invention, therefore, provides a novel method for the purposes as previously mentioned such that a compensation signal for said primary quantity of error, a signal representative of the minimum aperture and the like are transmitted from the lens to the camera body to achieve more accurate exposure control or display of diaphragm value and/or shutter speed.